AEM Wideband sensor replacement

Hi All,
My AEM wideband O2 sensor has **** the bed. I first have to dig out my paperwork to see if it uses the 4.2(Earlier) or 4.9 sensor. My question is AEM want over $100 for their sensor. They show them on Ebay for around $38 free shipping. Just curious if anyone has been down this road and how did things work out.
Thanks